Aug. 20, 2010 -- Exposure in the womb to pesticides known as organophosphates may increase the chance that children, especially boys, will develop attention problems by age 5, a study shows.

The research is published in Environmental Health Perspectives.

Researchers followed more than 300 children who took part in the Center for the Health Assessment of Mothers and Children of Salinas (CHAMACOS) study. It was designed to look at how exposure to organophosphate pesticides affects reproductive health.

The researchers measured levels of the breakdown products from these pesticides in the mother's urine twice during pregnancy. Children were followed up at 3.5 years and at five years to see if they showed any symptoms of attention deficit hyperactivity disorder (ADHD). ADHD is marked by inattention, impulsivity, and hyperactivity. Children with ADHD don't do as well in school or in social situations as their peers without ADHD.

Pesticides and ADHD Risk

Moms who had higher concentrations of metabolites or breakdown products of these pesticides in their urine during pregnancy were more likely to have children who showed signs of attention problems by age 5, the study showed. The risk was more pronounced in boys than girls.

The children in this study lived in agricultural Salinas Valley, Calif. They had greater than average exposure to the organophosphate pesticides studied.

"It is worth looking at this more carefully and conducting more research on this topic since low-level exposure to pesticides and pesticide residues in food is quite common," says study researcher Amy Marks, MPH, who was a research analyst at the University of California at Berkeley's School of Public Health when the new study was conducted.

Other classes of pesticide compounds should be looked at as well, Marks says in an email. "Given the impact and prevalence of attention disorders in children (and adults), finding potential opportunities for prevention is important."

Wash Fruits and Veggies to Get Rid of Residue

"We are not suggesting that people stop eating their fruits and vegetables," she says. "Practically speaking, some things that concerned parents and parents-to-be can do is to wash their produce thoroughly and to buy organic, if this option is available and affordable to them," she says. The group plans to study whether the effects of exposure to organophosphates on attention persist in older children.In a related study slated to appear in the same journal, researchers found that some children may be more vulnerable to the effects of these pesticides than others. Children with lower levels of an enzyme called paraoxonase 1 (PON1), which breaks down organophosphates, were more likely to develop neurologic developmental delays than their peers who had higher levels of this enzyme.

The findings "provide another critical piece of evidence linking prenatal exposure to organophosphate pesticides with ADHD problems, demonstrating the persistence of adverse effects well into the preschool years," says Virginia A. Rauh, ScD, deputy director of the Columbia Center for Children's Environmental Health in New York City, in an email.

The new report is consistent with other studies in the literature, says Rauh, whose institution is also conducting similar studies in New York City children. "This adds to the growing body of epidemiologic and experimental evidence showing worrisome links between organophosphate exposure, at levels common among U.S. children, and ADHD prevalence."

Jeff Stier, the associate director for the American Council on Science and Health, a New York City-based nonprofit consumer health education group, takes issue with the new study findings and the reasoning behind some of the action points that the researchers suggest.

The "warning to consumers that we wash produce to prevent pesticide exposure is completely beyond the scope of the study, which evaluated agricultural workers, not consumers," he says.

"We should wash produce before eating it to lower risk of food-borne illness, but not to reduce the imagined risk that trace pesticides would otherwise cause ADHD," he says. "I'm concerned that studies like this will have the effect of causing parents to fear feeding healthy fruits and vegetables to their children."